AwesomeWM: Alternative bindings setup

The default rc.lua from the Awesome window manager uses a lot of
globalkeys = awful.util.table.join(...) code.

I disliked this because …

they used functions to join the bindings. And in Lua, the parameters
of a function cannot end with a trailing comma. Often when I moved
an entry around, I ended up with a pointless syntax error because of
a trailing comma — or a missing comma between arguments.

adding elements by joining seems somewhat complex

adding logic, e.g. only adding a keybinding under specific
circumstances is suddenly more difficult

So let’s change this …

Note: the following works with AwesomeWM v4.0. I used v4.0-105-gbfb35349.